Ever wondered why sunburns hurt so much? Well, researchers believe that the pain may be the doing of a molecule called CXCL5, which seems to control sensitivity to pain from UVB radiation.

You may recall that the sun emits UVA, UVB and UVC rays. UVC is the most harmful but is blocked by the ozone layer, while UVA and UVB both breach the earth’s atmosphere and can affect human health.

Scientists have known CXCL5 is one of a family of proteins called chemokines. They promote healing by recruiting immune cells to the injury. But now, the latest study shows that CXCL5 also stimulates pain receptors at the injury site.

Researchers exposed small areas of volunteers’ skin to UVB rays and at the peak of the sunburn, took small tissue samples. They found a lot more CXCL5 in the sunburned skin compared to unburned skin. It was especially high in people who complained the most about pain.

Experimenting further with rats, researchers injected them with pure CXCL5. Their skin became hypersensitive to touch, partly because CXCL5 recruits inflammatory immune cells called neutrophils and macrophages.

These cells, in turn, secrete more CXCL5 and other molecules involved in pain stimulation. To see if, by counteracting CXCL5, the pain would subside, researchers injected antibodies against the molecule, and voila! the pain was reduced.

What’s significant about the findings is that it suggests CXCL5 and proteins like it could be involved in persistent pain that comes with other ailments such as osteoarthritis or bladder infections.

Learning how these molecules work could help scientists design new drugs for people who suffer from chronic pain.

Sunwise: UV radiation
The Environmental Protection Agency website provides information on UV radiation as part of its SunWise progam, which aims to educate kids and their parents about sun exposure. It has links to extensive educational resources. They (and we) remind readers and listeners that UV radiation from the sun and from tanning beds is classified as a human carcinogen according to the US Department of Health and Human Services and the World Health Organization.

Understanding UVA & UVB
The Skin Cancer Foundation provides excellent resources, including a wonderful explanation of the differences between and similarities of UVA and UVB rays. The information highlights the dangers of both outdoor and indoor tanning, which both increase the risk of developing skin cancers including melanoma.